Effects of microplastics on greenhouse gas emissions and microbial communities in sediment of freshwater systems

Microplastics can regulate greenhouse gas emissions from environmental systems and affect microbes in the environment. However, the effect of microplastics in freshwater sediment system is still not well studied. In this paper, polyethylene terephthalate (PET) particles with six different diameters of 5-2000 mu m were added to freshwater sediment, PET exposing for 90 days was carried out and its effect on greenhouse gas emissions, nutrients cycle and microbial communities were studied. In the 5 mu m experimental group, carbon dioxide (CO2) emissions were significantly promoted in the 7-30 days and nitrogen monoxide (N2O) emissions were significantly promoted in the 7 days after cultivation. Microplastics in the range of 300-800 mu m significantly promoted CO2 emissions after three days of culture. In addition, microplastics increased the total organic carbon (TOC) content in freshwater sediment and changed microbial diversity, especially increased the microorganisms capable of degrading complex organics such as Saprospiraceae. There was a positive correlation between N2O emission and nitrate (NO3-) content in sediment after 3 days of culture, while greenhouse gas emission was mainly related to TOC content after 90 days of culture. These results showed that microplastics could affect the carbon and nitrogen cycling process of shallow lake ecosystem.